The invention has been made in the field of magnetic field antennae used for inductive power transmission. Principally, it is possible to transmit power and information via electric or magnetic dipoles. In this process, electromagnetic waves or mostly electric or magnetic fields are generated depending upon the control circuit. It would be advantageous if no electromagnetic waves are radiated and if only magnetic fields are generated; this would avoid the influence on the organic web around the antenna. Another advantage would be that relatively high energies will be transmitted to a magnetic antenna without a galvanic coupling because of the radiation of magnetic fields and/or inductive coupling. The effect of such a coupling is restricted to a very small area less than approx. Im. In spite of this, there are several application possibilities for such a transmission.
Apart from the commonly used soft ferrites, most of the known soft magnetic powder composite materials can be used as pressed magnet cores. For example, these can be made up of iron powder. With magnet cores of such type, an effective permeability ranging from 10 to 30 can be achieved. Corresponding saturation inductions can range from 1.0 to 1.4 T. Apart from this, powder composite materials made from soft magnetic crystalline iron-aluminum-silicone alloys and iron-nickel alloys are known; application frequencies of more than 100 kHz can be achieved with these.
A disadvantage of such composite materials and ferrites is that the pressing technologies only allow simple geometric forms and that the resultant magnet cores are relatively brittle and likely to break. Also, the corresponding magnetic properties are very much dependent upon the temperature, which makes the use of resonant circuits more difficult.
According to DE 19846781 A1, magnet cores are known, which are formed with the injection casting method from plastic (which can be injection cast) and a nano-crystalline alloy.
Corresponding nano-crystalline alloys are also described in, for example, EP 0271657 A2 and EP 0455113 A2. Such alloys are manufactured in the form of thin alloy strips, for example, with the quick-setting technology. These alloys are initially amorphous and are hence, subjected to a heat treatment so that a nano-crystalline structure can be obtained. Such alloys can be ground to alloy powders with particle size less than 2 mm. Usually, these so-called flakes have a thickness ranging from 0.01 to 0.04 mm and width and length ranging from 0.04 to 1 mm per particle. With the help of plastics, these flakes can be processed to form composite materials, whereby saturation magnetizations of more than 0.5 Tesla and permeability ranging from 10 to 200 can be obtained. A method of forming such magnet cores is described in WO 0191141 A1.
In EP 0762535 A1, there are antennae made up of soft magnetic powder composite materials, e.g. amorphous alloys, for transponders. Such antennae are used for exchanging information. They ensure a fail-safe exchange of information over an area of several meters as well as less interference with metallic objects in the vicinity of the antennae.